Testosterone supplements are products that increase the male sex hormone testosterone, which governs muscle mass, aggression and secondary sexual characteristics in men 3. Prohormones, testosterone boosters and estrogen blockers are all different types of testosterone supplements 3. Each has its own list of potential side effects.

Prohormones and Steroids

Supplementing with prohormones, or the illegal form known as anabolic steroids, can cause many serious side effects. Prohormones are chemicals that convert to testosterone or testosterone-like analogues in the body 3. Examples of prohormones are TREN, androstenedione and DHEA. Increasing testosterone levels by unnatural means can throw off the delicate hormonal balance of the body 3. Side effects may include:

• hair loss
  
• gynecomastia (male breast enlargement)
  
• acne
  
• hypertension
  
• testicular atrophy
  
• prostate enlargement
  
• liver damage
  
• loss of libido

Of all the testosterone supplements, prohormones have the most serious side effects 23. However, DHEA can be a useful hormone replacement supplement for men experiencing andropause, or age-related low testosterone levels 3.

Testosterone Boosters

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Testosterone boosters are natural substances that can coax the body to produce more lutenizing hormone, a messenger hormone secreted by the pituitary gland that signals the testicles to produce more testosterone 3. In addition, testosterone boosters may unbind bound testosterone, creating more usable free testosterone 3. Testosterone boosters include:

• tribulus terrestris
  
• fenugreek extract
  
• longjack
  
• avena sativa
  
• safed musli
  
• coleus forskohlii as well as various combinations of these herbs 3

The increase in total endogenous (body made) testosterone can elicit some of the same side effects as using prohormones and steroids, though generally milder 23. These side effects may include gynecomastia, hair loss, acne and prostate enlargement.

Estrogen Blockers

Estrogen blockers increase testosterone by inhibiting the hormone from converting to estrogen 3. Anti-estrogen substances are also known as anti-aromatase. Aromatase is the enzyme that converts testosterone into the female hormone estrogen 3. Over-producing female hormones will not get you any closer to your fitness goals. Two popular anti-aromatase products are 6-OXO and Novedex XT. According to Jerry Brainum, a noted fitness expert, Novedex XT increased free testosterone 625 percent in an eight-week study 3. However, it also increased the production of DHT (dihydrotestosterone) by a whopping 566 percent. 6-OXO increased free testosterone by 90 percent, accompanied by a 192 percent increase in DHT 3. DHT is responsible for such side effects as acne, prostate enlargement and hair loss. Inhibiting aromatase seems to contribute to these side effects via increased 5-alpha reductase enzyme.