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Primobolan (Primo)

Primobolan (known as Metenolone enanthate, Primo) is an anabolic androgenic steroid (AAS) that comes in both injectable and oral form. It is used by bodybuilders who want something with few side effects, no estrogenic activity, and who pursue lean muscle mass. Primo is considered 'weak' and this is true to some extent; you will not break lifting records or gain a lot of weight on this steroid, but you will gain slow and quality mass over many weeks.

It is one of the most pricey steroids available today, and one that is misunderstood by many in the bodybuilding community. I believe that those who have built a strong base naturally after many years of training will appreciate primobolan as the icing on the cake. It is a safe compound that doesn't interfere with sleep, doesn't cause blood-pressure symptoms, and does not represent any sort of gynecomastia/estrogen risks.

primobolan amps bayer

Fig 1. Bayer Primobolan

Table of Contents


Primobolan was extremely popular in the 70's during the 'golden age' of bodybuilding, and it is said to be Arnold Schwarzenegger's favorite steroid to run.

Nowadays, its popularity has been darkened by fakes flooding the market, and the steep cost. As a result, more bodybuilders are choosing to go the harsher route with such steroids as trenbolone, which are far cheaper and less likely to be faked. This makes primo underrated because many users are impatient and do not understand the concept of slow and quality gains, and they would rather get fast and sloppy gains. However, there seems to be a comeback of this compound as people have started shying away from brutal side effects of other steroids.

Furthermore, another problem is that pharmaceutical grade primobolan has extremely potent post injection pain (PIP) and only comes in 100mg/ml ampules. This means you would be required to make several very painful injections every week to get enough primo in your system. To help solve this problem there has been the increase in underground labs (UGL), which make primobolan in 200-300mg/ml vials using other oils to make PIP less pronounced.

Medical Uses

While most steroids were originally developed for some sort of medical purpose first and then became abused in the bodybuilding community, primobolan is one of the only steroids that was actually developed solely for bodybuilders. However, primobolan is banned by the FDA, so there are no medical uses aside from 'off label', meaning that it can still offer some significant benefits in the treatment of such conditions as AIDS.


Some of the top AIDS doctors in the world have begged the FDA to make metenolone enanthate available because of its excellent immune system boosting properties. When cycling primo, you may notice that everyone around you will get a cold or flu, but you will not, and this is not a coincidence. AIDS patients find primobolan to be perfect for them to prevent mass wasting without harsh side effects of other AAS, like anadrol for example.


Alex Rodriquez and Barry Bonds are both considered two of the best major league baseball players of their era. However, both of them reported to test positive for primobolan according to Sports Illustrated. "A-rod" claimed he had purchased primo legally while visiting the Dominican Republic. Ironically, primo is not available over the counter in that country anyway.

It would make sense that athletes would choose primo because of its low side effects, lack of water retention, and shorter detectable times vs. other injectables.


Primobolan is a Dihydrotestosterone (DHT) derived compound. DHT is an androgen hormone and sex steroid that is synthesized by the 5a-reductase enzyme in the in the hair follicles, prostate adrenal glands, and testes, which gives males man-like features.

Unlike testosterone, DHT does not convert to estrogen. Therefore, DHT levels can rise in the body without estrogen increase, avoiding estrogenic side effects. unlike testosterone, which can lead to estrogenic side effects.


Sex hormone binding globulin (SHBG) is a protein that binds to sex steroids and renders them inactive for as long as SHBG is bound to them. Free testosterone is what matters, so the higher you can get that relative to total testosterone the more benefits you can expect; this is referred to as bound vs. unbound testosterone.

Being a DHT derivative, Primobolan will bind to SHBG increasing free testosterone, which is why it works so well as part of a steroid stack instead of alone. For this reason, using primobolan alone will be a waste of its full potential, and you should always stack primobolan in a steroid cycle.

Injectable vs. Oral Primo

Injectable primobolan is superior to oral primo in many ways. Oral primo results are not very good simply because a large amount of the active substance will be destroyed by the liver. Since it is not a 17aa oral, the dosages have to be run much higher, which makes it expensive for some users. Hence, I recommend you run injectable primo if you want to get the cheapest and best results.

Use and Dosage

Primobolan should be used as part of a steroid stack and it is recommended the injectable version be used at a minimum of 400-500 milligrams (mgs) per week for best results with men. The oral version can be used 75-100mg's per week.

There is some debate on female use and, in my view, women should never use DHT derivative compounds due to the virilization risk, unless they are extremely experienced.

Side Effects

Primobolan is very gentle when it comes to side effects, which makes it a fantastic AAS to stack with other harsh compounds. Just like with all hormones, the main side effect is natural testosterone suppression. Therefore, a post cycle therapy needs to be implemented. Other side effects, such as hair loss due to its DHT properties, are possible.

If primo is abused at over a gram (1000mgs) a week, more sides (organ strain for instance) will occur. It is foolish to assume that just because primobolan is considered 'weak' it shouldn't be respected. Remember, it is still a potent steroid and needs to be run correctly with a good plan.

Detection and Half Life

Injectable primobolan has the enanthate ester attached to it, so the half life would be approximately 10.5 days. This does not mean that the compound will be out of your system in 10.5 days after your last injection. Rather, it means that after that time-span, half of what you injected will be leftover, so you can expect primo to keep working for several weeks after last injection as it tapers out of your system. It is detectable only for 5 weeks.

Oral primobolan's half life is about 5 hours and it will be detected up to 5 weeks.


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Written by
Mike Snow is an NPC champion with 18 shows under his belt. He took multiple 1st placing at NPC regional bodybuilding shows. He has a diploma from Stanford SCHE exercise and Physiology courses. He holds NASM and ACE personal training certifications and he's working to get his ISSA certification this year.

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