Human Effect Matrix
The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects l-dopa has on your body, and how strong these effects are.
|Grade||Level of Evidence [show legend]|
|Robust research conducted with repeated double-blind clinical trials|
|Multiple studies where at least two are double-blind and placebo controlled|
|Single double-blind study or multiple cohort studies|
|Uncontrolled or observational studies only|
Level of Evidence
? The amount of high quality evidence. The mo re evidence, the more we can trust the results.
Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
|Penile Girth||Minor||- See 2 studies|
|Libido||-||- See study|
Scientific Research on L-DOPA
Click on any below to expand the corresponding section. Click on to collapse it.
L-Dopa is an amino acid supplement that produces dopamine in the body after oral ingestion.
L-Dopa is found in:
Mucuna Pruriens (Young seeds have 53.31+/-0.03mcg/g (0.53%) to 119.2 ± 6.9mcg/g (1.19%)) Seeds tend to increase in L-Dopa content as they mature, up to an average of 3.1-6.1% with the highest recorded value of 9%. Leaves of M.Pruriens have around 0.5%.
Tamarindus indica (Seeds have 377.6 ± 13.9mcg/g, or 3.78%)
Entada scandens (Seeds have 167.2 ± 6.9mcg/g, or 1.67%)
Bauhinia variegata (Seeds have 291.2 ± 6.9mcg/g, or 2.91%)
Canavalia gladiata (Seeds have 422.4 ± 12.0mcg/g, or 4.22%)
Vigna aconitifolia, unguiculata, and vexillata at around 0.2-0.58%
The exact number in the sources are variable, as is the nature of plants. The general notion should be that C.Gladiata, T.Indica, and S.Binpinosa appear to be quite high as well as Mucuna Pruriens; the standard source of L-Dopa in supplements.
L-Dopa, when oxidized, can form bonds with sulfur containing compounds (such as cysteine) to polymerize with other amino acids and lower bioavailability of protein when L-Dopa is consumed via foods.
L-Dopa can be destroyed in legumes by cooking and soaking with alkaline solutions. Although it can also be destroyed with basic cooking, toasting does not appear to destroy L-Dopa from Mucuna Pruriens.
Chronic usage of L-DOPA is associated with a greater bioavailability of future L-DOPA ingestion.
A dose of 1000mg/kg bodyweight L-DOPA in rats (human dose equivalent 160mg/kg) is associated with an increased circulating testosterone level in rats after 7-14 days, possibly secondary to Luteinizing Hormone. The only other study investigating testosterone levels is one done in Japanese Quails, which shows increased testosterone possibly secondary to dopaminergic influence of the testes.
The theory of dopamine precursors increasing testosterone is there, but the topic has not been investigated into with any depth.
In rats, an oral dose of 1000mg/kg bodyweight (human dose equivalent 160mg/kg) increases Lutenizing hormone after 4 hours yet it returns to baseline after 8 hours. This effect was not seen at 200mg/kg (32mg/kg humans) nor any dose below, ingestion of 500mg L-DOPA in humans, according to one study, actually causes a slight but significant decrease in circulating Luteinizing Hormone levels over the 2 hours following treatment.
One study measuring cortisol levels after ingestion of 500mg L-DOPA found that the decrease seen in cortisol was not significantly different from placebo. A more recent study in persons with Parkinson's disease suggests a reduction in cortisol levels after ingestion of 200mg L-DOPA (paired with 50mg benserazide).
L-DOPA administration at 800mg daily for 7 days in healthy men (no complaints of penile problems) is associated increased penis tumescence (thickness from bloodflow); however, its effects were most significant when serum testosterone was greater than 17.5pg/mL suggesting the effect is androgen-dependent. In youth (20-30) it also increased maximum penile girth. This effect may be mediated through dopamine receptor agonism.
Increased dopamine appears to increase thickness of the flaccid penis, and this applies to L-DOPA supplementation due to increasing dopamine. There are no studies on erect penis thickness
Interestingly, with Levodopa therapy in Parkinson's Disease a possible side-effect is Hypersexuality associated with excessive dopaminergic firing via dopaminergic agonism. It is more commonly associated with chemical dopamine agonists rather than levodopa, however. It is one of the many side effects associated with compulsivity from dopamine agonism, just the sexual manifestation.
In healthy men and women, 100mg single administration of L-DOPA was able to augment magnitude of T-reflex (used to measure physical responses to orgasm) in men, although 100mg L-DOPA was ineffective at increasing libido or sexual arousal; possibly related to dopamine's role in the energetic aspects of motivated behaviour, by acting on the oxytocinergic neurons in the PVN of the hypothalamus. 3 men reported penile erection during the control (non-sexual) film used, an amusing side-effect.
Case studies of persons using L-DOPA at dosages exceeding 2.5g note hypersexuality and more frequent (sometimes inappropriately timed) erections, although this subset of case studies are intertwined with psychiatric disorders. Dosages exceeding 6g were associated with increased aggressiveness.
Dopamine is definitely involved in Libido and the physical response to sexual excitation, although L-DOPA treatment may not be potent enough to be clinically relevant in isolation it may be valuable in combination with other compounds. Whether L-DOPA supplementation will lead to increase sexuality in otherwise healthy persons is not known.
Women who have PCOS (excess circulating androgen levels) may alter the effects of oral L-DOPA on hormones, lowering the increase in growth hormone seen after L-DOPA in women without PCOS. Interestingly, these effects are also seen in obese individuals. The former conditions is characterized by higher insulin and IGF-1 levels, which may play a role. The latter conditions, obesity, seems to reduce the GH secretion from L-DOPA via elevated serum fatty acids (triglycerides). These elevated TGs hinder growth hormone secretion at rest and reducing their levels can enhance the efficacy of compounds that stimulate GH release.
L-DOPA is rapidly converted into dopamine in peripheral tissue (ie. not the brain) via dopamine decarboxylase enzymes, and this is the reason for its common therapeutic pairing with carbidopa; under these conditions, the next major pathway that mediates conversion of L-DOPA (albeit a methylation process to 3-O-methyldopa) would be via catechol-o-methyltransferase (COMT) which EGCG from the green tea catechins is known to inhibit and in some patients pharmaceutical COMT inhibitors such as tolcapone or entacapone are also recommended.
It seems many COMT inhibitors can suppress this secondary conversion of L-DOPA into 3-O-methyldopa, including (+)-catechin (3.7+/-3.2μM), (-)-epicatechin (10.7+/-6.7μM), and quercetin (1.9+/-0.4μM) although only (+)-catechin worked in vivo at 400mg/kg injections where L-DOPA concentrations in plasma are unaffected yet 3-O-methyldopa is decreased.
It seems that after the dopamine decarboxylase enzymes are taken care of, the COMT enzyme may become (relatively) more active and methylate L-DOPA. COMT inhibitors such as EGCG or (+)-catechin can reduce this reactions
S-adenosyl Methionine (SAMe) is a small molecule involved in a process known as methyl donation, seen as an intermediate in one pathway of cellular maintenance.
One study in children with a dopamine deficeincy being treated with Levodopa noted that supplementation of Levodopa caused a decrease in concentrations of SAMe in cerebrospinal fluid with an increase in 3-methoxytyrosine.
L-DOPA is able to cause abnormal motor control (Drug-Induced Dyskinesia), which is seen as a common side effect when L-DOPA is used chronically for treating Parkinson's Disease. A loss of Dopamine in the Basal Ganglia (a brain structure) is associated with a process called dyskinogenesis; the production of dyskinesia, or involuntary movement of skeletal muscles.
Dyskinesis is associated with an increased expression of dynorphin in the striatum and increases of the mRNA of both preproenkephalin A and prodynorphin (preproenkephalin B) in the striatum.
On the neuronal side of things, it is hypothesized that drug-induced dyskinesia is due to sensitization of the D1 (dopamine-1) receptors on the MSN neurons in the striatum. High sensitization leads to intermittent and excessive cAMP signalling cascades, and involuntary movement.
Interestingly, tolerance to caffeine is associated with desensitized D1 receptors on this neuronal cluster and may be used to manage symptoms of involuntary motor control associated with L-DOPA supplementation.
For healthy persons, the importance of being concerned with Levodopa induced dyskinesia is unknown. The chance of dyskinesia appears to increase with disease pathology, and correlates with destruction of dopamingergic neurons typical of Parkinsons and age; increasing from 40% to 80% over the course of 5 years of Parkinsons. In primates it has been shown that dyskinesia is not induced in healthy controls at the same dose that induces dyskinesia in those with less dopaminergic neurons and Parkinsons progression. Another study done on squirrel monkeys suggested that nigrostriatal dopaminergic neuron loss is a prerequisite for dyskinesia, and that Levodopa-induced dyskinesia can not occur in healthy controls.
Major concern associated with L-DOPA, but appears to pretty much only be relevant to those suffering from Parkinson's Disease or similar neurodegeneration. Most likely not a concern for healthy persons using L-DOPA in moderation
- Gautam B, et al. Bioactive compounds extracted from Indian wild legume seeds: antioxidant and type II diabetes-related enzyme inhibition properties. Int J Food Sci Nutr. (2012)
- Vadivel V, Pugalenthi M. Studies on the incorporation of velvet bean (Mucuna pruriens var. utilis) as an alternative protein source in poultry feed and its effect on growth performance of broiler chickens. Trop Anim Health Prod. (2010)
- The phytochemistry, toxicology, and food potential of velvetbean (Mucuna Adans. spp., Fabaceae).
- García Echeverría CL, Bressani R. Effect of different cooking treatments of Mucuna beans on its L-Dopa content. Arch Latinoam Nutr. (2006)
- Tomita-Yokotani K, et al. Distribution of L-DOPA in the root of velvet bean plant (Mucuna pruriens L.) and gravity. Biol Sci Space. (2004)
- Ramya KB, Thaakur S. Herbs containing L- Dopa: An update. Anc Sci Life. (2007)
- L-DOPA bearing plants.
- Comperative nutritional evaluation of little known legumes, Tamarindus indica, Erythrina indica and Sesbania bispinosa.
- Nutritional assessment and chemical composition of the lesser known tree legume, Acacia leucophloea (Roxb.) Willd.
- Dahouda M, et al. Nutrient digestibility of Mucuna (Mucuna pruriens var. utilis) bean in guinea fowl (Numida meleagris, L): Effects of heat treatment and levels of incorporation in diets. Br Poult Sci. (2009)
- Muhlack S, et al. Chronic levodopa intake increases levodopa plasma bioavailability in patients with Parkinson's disease. Neurosci Lett. (2004)
- Yamada T, et al. Effect of chronic L-dopa administration on serum luteinizing hormone levels in male rats. Toxicology. (1995)
- Prasad SK, Qureshi TN, Qureshi S. Mucuna pruriens seed powder feeding influences reproductive conditions and development in Japanese quail Coturnix coturnix japonica. Animal. (2009)
- Root AW, Russ RD. Effect of L-dihydroxyphenylalanine upon serum growth hormone concentrations in children and adolescents. J Pediatr. (1972)
- Boden G, Lundy LE, Owen OE. Influence of levodopa on serum levels of anterior pituitary hormones in man. Neuroendocrinology. (1972)
- Müller T, Welnic J, Muhlack S. Acute levodopa administration reduces cortisol release in patients with Parkinson's disease. J Neural Transm. (2007)
- Horita H, et al. Effects of levodopa on nocturnal penile tumescence: a preliminary study. J Androl. (1998)
- Lal S, et al. Effect of apomorphine, a dopamine receptor agonist, on penile tumescence in normal subjects. Prog Neuropsychopharmacol Biol Psychiatry. (1984)
- Bostwick JM, et al. Frequency of new-onset pathologic compulsive gambling or hypersexuality after drug treatment of idiopathic Parkinson disease. Mayo Clin Proc. (2009)
- Klos KJ, et al. Pathological hypersexuality predominantly linked to adjuvant dopamine agonist therapy in Parkinson's disease and multiple system atrophy. Parkinsonism Relat Disord. (2005)
- Both S, et al. Effect of a single dose of levodopa on sexual response in men and women. Neuropsychopharmacology. (2005)
- Salamone JD, Correa M. Motivational views of reinforcement: implications for understanding the behavioral functions of nucleus accumbens dopamine. Behav Brain Res. (2002)
- Giuliano F, Allard J. Dopamine and sexual function. Int J Impot Res. (2001)
- Angrist B, Gershon S. Clinical effects of amphetamine and L-DOPA on sexuality and aggression. Compr Psychiatry. (1976)
- Lee EJ, et al. Growth hormone response to L-dopa and pyridostigmine in women with polycystic ovarian syndrome. Fertil Steril. (1993)
- Lee EJ, et al. Reduced growth hormone response to L-dopa and pyridostigmine in obesity. Int J Obes Relat Metab Disord. (1994)
- Cordido F, et al. Impaired growth hormone secretion in obese subjects is partially reversed by acipimox-mediated plasma free fatty acid depression. J Clin Endocrinol Metab. (1996)
- Lee EJ, et al. Acipimox potentiates growth hormone (GH) response to GH-releasing hormone with or without pyridostigmine by lowering serum free fatty acid in normal and obese subjects. J Clin Endocrinol Metab. (1995)
- Nagai M, Conney AH, Zhu BT. Strong inhibitory effects of common tea catechins and bioflavonoids on the O-methylation of catechol estrogens catalyzed by human liver cytosolic catechol-O-methyltransferase. Drug Metab Dispos. (2004)
- Männistö PT, Kaakkola S. Catechol-O-methyltransferase (COMT): biochemistry, molecular biology, pharmacology, and clinical efficacy of the new selective COMT inhibitors. Pharmacol Rev. (1999)
- Toulouse A, Sullivan AM. Progress in Parkinson's disease-where do we stand. Prog Neurobiol. (2008)
- Kang KS, et al. Beneficial effects of natural phenolics on levodopa methylation and oxidative neurodegeneration. Brain Res. (2013)
- Surtees R1, Hyland K. L-3,4-dihydroxyphenylalanine (levodopa) lowers central nervous system S-adenosylmethionine concentrations in humans. J Neurol Neurosurg Psychiatry. (1990)
- Nadjar A, Gerfen CR, Bezard E. Priming for l-dopa-induced dyskinesia in Parkinson's disease: a feature inherent to the treatment or the disease. Prog Neurobiol. (2009)
- Hanrieder J, et al. L-DOPA-induced dyskinesia is associated with regional increase of striatal dynorphin peptides as elucidated by imaging mass spectrometry. Mol Cell Proteomics. (2011)
- Nisbet AP, et al. Preproenkephalin and preprotachykinin messenger RNA expression in normal human basal ganglia and in Parkinson's disease. Neuroscience. (1995)
- Henry B, et al. Increased striatal pre-proenkephalin B expression is associated with dyskinesia in Parkinson's disease. Exp Neurol. (2003)
- Calon F, et al. Increase of preproenkephalin mRNA levels in the putamen of Parkinson disease patients with levodopa-induced dyskinesias. J Neuropathol Exp Neurol. (2002)
- Feyder M, Bonito-Oliva A, Fisone G. L-DOPA-Induced Dyskinesia and Abnormal Signaling in Striatal Medium Spiny Neurons: Focus on Dopamine D1 Receptor-Mediated Transmission. Front Behav Neurosci. (2011)
- Prediger RD. Effects of caffeine in Parkinson's disease: from neuroprotection to the management of motor and non-motor symptoms. J Alzheimers Dis. (2010)
- Frequency of levodopa-related dyskinesias and motor fluctuations as estimated from the cumulative literature.
- Dopamine agonist-induced dyskinesias are correlated to both firing pattern and frequency alterations of pallidal neurones in the MPTP-treated monkey.
- Boyce S, et al. Nigrostriatal damage is required for induction of dyskinesias by L-DOPA in squirrel monkeys. Clin Neuropharmacol. (1990)