As the prostate gland enlarges, it causes pressure on the urethra, the outlet from which urine flows outward. There are certain muscle cells around the urethra, especially where it starts by the bladder. These muscle cells can sometimes constrict (increase in tone) and contribute to the narrowing of the urethral outlet. There are certain receptors on these muscle cells called alpha-receptors. When a medicine is ingested that stimulates these alpha-receptors, the muscle tightens and it becomes even more difficult to urinate. Certain amphetamine-like medicines, such as diet, pills or cold medicines (pseudoephedrine), are a classic example: they make it difficult to urinate. On the other hand, there are drugs that block these receptors and these are often prescribed to patients who have difficulty urinating. These medicines are called alpha-blockers, and they generally provide improvement within two weeks after the initiation of therapy. Compare this to 5-alpha-reductase inhibitors that take much longer to reach their maximum effect.

Alpha-blockers were originally prescribed for the treatment of high blood pressure. There are tiny muscles around blood vessels that can contract and thus elevate blood pressure. Alpha-blockers work by relaxing these muscles and reduce blood pressure.

There are also tiny muscles present surrounding the urethra. Since alpha-blockers are also able to relax these muscles, they work quickly to improve symptoms. However, they are not curative. They don't lead to reversal of prostate enlargement since they don't attack the underlying problem. When alpha-blockers are stopped, prostate symptoms quickly return. However, if quick temporary relief from an annoying case of prostate enlargement is wanted, alpha-blockers are a good option. They can ease the symptoms until SP and other herbs are started. The herbal medicines will work slower, but in the meantime the number of times the patient must wake up at night to visit the bathroom is reduced.

The best known of the alpha-blockers are terazosin, prazosin, alfuzosin, and doxazosin. Side effects of alpha-blockers include dizziness, fatigue, a drop in blood pressure on standing, and weakness. These can occur in more than 20% of users. These medicines require caution, especially if the patient is currently on pills that lower blood pressure.

New alpha-blockers are constantly being introduced to the market. Tamsulosin (Flomax), an alpha-blocker for the therapy of BPH, received approval by the FDA in 1997. The recommended dosage is 0.4 mg once daily. Common side effects include dizziness and abnormal ejaculation.

In addition to the above, other medicines, hormones and nutrients may have the ability to inhibit the conversion of testosterone to DHT, or somehow shrink the prostate gland. These include spironolactone, bromocriptine, and others. These medicines are not commonly used since their full effects are currently not fully determined.