Levodopa in healthy individuals

[spephspeph]

What effects would levodopa have in people who don't suffer from parkinsonian symptoms, with and without carbidopa?

 

[sekio]

The side effects of L-DOPA may include, but not limited to:

Hypotension, especially if the dosage is too high
Arrhythmias, although these are uncommon
Nausea, which is often reduced by taking the drug with food, although protein interferes with drug absorption
Gastrointestinal bleeding
Disturbed respiration, which is not always harmful, and can actually benefit patients with upper airway obstruction
Hair loss
Disorientation and confusion
Extreme emotional states, particularly anxiety, but also excessive libido
Vivid dreams and/or insomnia
Auditory and/or visual hallucinations
Effects on learning; there is some evidence that it improves working memory, while impairing other complex functions
Somnolence and narcolepsy
A condition similar to stimulant psychosis

Although there are many adverse effects associated with L-DOPA, in particular psychiatric ones, it has fewer than other antiparkinsonian agents, such as anticholinergics and dopamine receptor agonists.

More serious are the effects of chronic levodopa administration in the treatment of Parkinson disease, which include:

End-of-dose deterioration of function
On/off oscillations
Freezing during movement
Dose failure (drug resistance)
Dyskinesia at peak dose
Possible serotonin depletion: Recent studies have demonstrated that use of L-DOPA without simultaneously giving proper levels of serotonin precursors depletes serotonin
Possible dopamine dysregulation: The long-term use of L-DOPA in Parkinson's Disease has been linked to the so-called dopamine dysregulation syndrome.[4]

Clinicians will try to avoid these side effects by limiting L-DOPA doses as much as possible until absolutely necessary.

So yeah, nothing good.

Most of these you shouldn't worry about unless you take carbidopa too, because L-dopa is rapidly decomposed outside the BBB and shouldn't have much of an effect on anything but blood pressure.

 

[/navarone/]

L-DOPA as a neurotransmitter precursor is much less safer than the analogous serotonin precursor 5-HTP.
There seems to be a different mechanism behind the enzymatic conversion where 5-HTP is metabolized just slightly above the 'ammount needed' by the brain while the excess remains either on standby or is excreted (at least from what I've heard), so there seems to be some sort of regulation. L-DOPA (toghether with carbidopa to avoid metabolism before crossing the BBB) on the other hand is converted very rapidly to dopamine and that could be dangerous depending on the ammount.
I've had some short regimen of L-DOPA and carbidopa in the past, obviously in minute ammounts.
Unless you have certain medical or psychiatric conditions where indiscriminately high dopamine levels are unrecommended, small doses can be safe though I would rather reccomend L-tyrosine as a safer and 'longer acting' precursor to dopamine i.e. eat a lot of poultry, fish, dairy products and protein rich foods.

 

[Hammilton]

I've taken L-dopa up to 25/100 carbidopa/l-dopa a day (a fairly low dose). I'm not exactly healthy, but for a person who is, I would worry that 3-O-Methyl-Dopa would accumulate and induce parkinsonian symptoms. Not a good idea.

I don't think it'd be dangerous in the short term, but in the long term, you've only got one brain, and this isn't going to get you high, so I'd avoid it. Reward vs. Risk really.