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L-arginine increases prolactin levels?

L-arginine increases prolactin levels?

So after seeing an off-hand comment by a poster on a bodybuilding forum, I decided to look this one up, it looks like he might’ve been right:

In addition, L-arginine infusion at rest increases plasma insulin, growth hormone, glucagon, catecholamines and prolactin.


Prolactin response to arginine in normal subjects and in patients with hyperthyroidism.

Onishi T, Itoh KF, Miyai K, Shima K, Kumahara Y.

The effect of arginine on serum prolactin concentrations was studied in 18 normal subjects and in 7 patients with hyperthyroidism in normal subjects, arginine infusion produced an increase of serum prolactin at least 6 ng/ml from the baseline, and the mean peak level (25.2 +/- 3.3 ng/ml, mean +/- SE) was significantly higher than the basal level (8.6 +/- 5.2 ng/ml, P less than 0.001). There was no significant difference in the peak levels between sexes. Unlike prolactin, concomitant serum thyrotropin levels did not change after the arginine infusion. In hyperthyroid patients, the increment of serum prolactin after arginine infusion at 30 min (3.9 +/- 1.5 ng/ml) was significantly lower than that of the normal controls which were matched by age and sex (17.1 +/- 4.4 ng/ml, P less than 0.05). After treatment when these patients were euthyroid, the increment of prolactin after arginine infusion at 30 min was significantly increased (16.3 +/- 4.3 ng/ml, P less than 0.05) and had reached the level of control subjects. These data indicate that the prolactin response to arginine in hyperthyroidism is diminished.

PMID: 1249182 [PubMed - indexed for MEDLINE]

So while the vasodilation properties are great, prolactin increase is DEFINITELY something we wouldn’t want. Thoughts?


Prolactin, from how I understand it, slows down your “reloading” time literally.

“You see, I don’t want to do good things, I want to do great things.” ~Alexander Joseph Luthor

I know Lewd Ferrigno personally.

Typical, seems like everything contradicts itself in one aspect or other.

Oops, sorry, I should’ve been a little more detailed on prolactin’s effects. Yeah, it increases the refractory period until you can go again, and it down-regulates the dopamine response to sexual stimuli (thus decreasing sexual arousal response). It can also potentially decrease testosterone levels.\

I don’t know to what degree it’s actually increasing prolactin, since if it was a very high amount we’d all be lactating.

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