ED Tablet Add-Ins: Oxytocin, L-Arginine, Pycnogenol and Caffeine

Below: which products contain which add-ins, what the studies found for each, and what that means when you compare prices. We make no claims for any add-in and give no doses.

Which ED products contain add-ins

Every product in this table is compounded. That means a pharmacy mixes it to order, and it is not FDA-approved. The FDA does not review a compounded product before it is sold.

MangoRx's own page describes its add-ins with care. It calls oxytocin "A hormone included in this compounded formula at your provider's discretion", and L-arginine "An amino acid included in this compounded formula" (MangoRx). Neither line claims a benefit. Apomorphine is a prescription drug rather than an add-in, so it has its own page: apomorphine for ED.

L-arginine for ED

L-arginine is an amino acid, a building block of protein. The body uses it to make nitric oxide, a gas that relaxes blood vessels. ED pills work further down that same path, which is why sellers pair the two.

L-arginine on its own has the most research of any add-in here. A 2019 review pooled 10 trials with 540 men. Its authors wrote that "Arginine supplements can be recommended to patients with mild to moderate ED" (Rhim et al., Journal of Sexual Medicine, PubMed, read 14 November 2026). They also noted that "The adverse effect rate in the arginine-treated group was 8.3%, and that in the placebo group was 2.3%, none of which were severe." A placebo is a dummy pill.

The 2024 review that ranked many supplements put L-arginine with tadalafil above tadalafil alone in some men. That review still described most supplements as not working. So the honest summary is: some support for mild ED, small trials, and no proof that the amount inside a compounded ED tablet adds anything.

Pycnogenol

Pycnogenol is a brand of pine bark extract. It is usually studied together with L-arginine. A 2023 review found that "Three studies with 184 patients were included" (Frontiers in Endocrinology review, PubMed, read 14 November 2026). The pair improved sexual function scores in mild to moderate ED. The authors added that "More randomized controlled trials are needed in the future". Randomized means the men are put in each group by chance.

Three studies is a small base. And in RxSpan's and DudeMeds' tablets, pycnogenol sits next to sildenafil or tadalafil, not next to L-arginine as in those trials.

L-citrulline

L-citrulline is another amino acid. The body turns it into L-arginine. One small study gave it to 24 men with mild ED. The authors concluded: "Although less effective than phosphodiesterase type-5 enzyme inhibitors, at least in the short term, L-citrulline supplementation has been proved to be safe and psychologically well accepted by patients" (Cormio et al., Urology, PubMed, read 14 November 2026). Phosphodiesterase type-5 inhibitors are the class that includes sildenafil and tadalafil.

So L-citrulline did less than an ED pill in that one study. No trial we found tested it inside a tablet that already holds tadalafil.

Caffeine

Caffeine appears in RxSpan's and DudeMeds' daily tadalafil blends. The main study is a survey, not a trial. Researchers looked at diet records from 3,724 US men in a national health survey. Men who drank about two to three cups of coffee a day were less likely to report ED. The authors said "these associations are warranted to be investigated in prospective studies" (Lopez et al., PLoS One, PubMed, read 14 November 2026).

A survey link is not proof of cause. Men who drink coffee may differ in other ways. Caffeine can also raise heart rate and cause jitters, which some men want to avoid.

Oxytocin for ED

Oxytocin is a hormone released during touch, closeness and orgasm. It is in MangoRx, BlueChew GOLD and SuperStrut products. Early lab research suggested it helped sexual behavior. Human studies have not borne that out.

A 2021 review of the research said that in men and women, "the results of these studies do not appear to confirm the facilitatory role of oxytocin" seen in lab research (Melis and Argiolas, International Journal of Molecular Sciences, PubMed, read 14 November 2026). Facilitatory means helpful. Most of those human studies used a nasal spray, not a tablet under the tongue.

What this means when you compare prices

An add-in can make a tablet cost more without making it work better. Compare the price per dose of a mixed tablet with plain generic sildenafil or tadalafil, both FDA-approved:

Prices checked November 14, 2026. Some men still prefer a mixed tablet for the form, the flavor or the idea of one product. That is a fair choice, as long as you know the add-ins have limited evidence. Our compounded ED medication guide explains how compounded products differ, and our ED pills compared guide covers the approved pills. Payment never moves a rank; see how we rank ED programs.