However, in contrast, a recent systematic review of published studies, the authors concluded that overall, the addition of testosterone to PDE-5 inhibitors might benefit patients with ED associated with testosterone levels of less than 300 ng/dL (10.4 nmol/L) who failed monotherapy.  A limitation of existing studies are their heterogeneous nature and methodological drawbacks.
Cialis is available in three strengths: 5mg, 10 mg, and 20 mg. Cialis can work in 30 minutes, but peak results usually take longer. Cialis has the advantage of a much longer period (24-36 hours) during which sexual ability is increased. The newest formulation of Cialis is the 5 mg dosage for daily use. The major advantage of daily dosing is that it allows for spontaneous sexual activity.
Oral medicines: The best known ED medications are the Big Three: Viagra (sildenafil citrate, made by Pfizer, Inc.), Levitra (vardenafil HCl, made by Bayer and GlaxoSmithKline), and Cialis (tadalafil, made by Eli Lilly). The three are chemically very similar, and all have proven very effective. Because they are effective, convenient, and relatively inexpensive (about nine dollars per pill), these medicines have become the treatment of choice for most men experiencing ED.
Erections occur in response to tactile, olfactory, and visual stimuli. The ability to achieve and maintain a full erection depends not only on the penile portion of the process but also on the status of the peripheral nerves, the integrity of the vascular supply, and biochemical events within the corpora. The autonomic nervous system is involved in erection, orgasm, and tumescence. The parasympathetic nervous system is primarily involved in sustaining and maintaining an erection, which is derived from S2-S4 nerve roots.
Many factors can contribute to sexual dysfunction in older men, including physical and psychological conditions, comorbidities and the medications used to treat them. Aspects of an ageing man’s lifestyle and behaviour and androgen deficiency, most often decreasing testosterone levels, may affect sexual function as well. A study of men between the ages of 30 and 79 years showed that 24% had testosterone levels below 300 ng/dL and 5.6% had symptomatic androgen deficiency.2
Many reasonable nonsurgical erectile dysfunction (impotence) treatment options exist, including external vacuum devices, medications (oral and topical), hormonal therapy, penile injection therapy, and intraurethral pellet therapy. Sex counseling to further improve one's sexual health and sex life is another option and is discussed in Living With Erectile Dysfunction.
However, a review of a United Kingdom medical record database found no evidence that the use of 5-alpha reductase inhibitors independently increase the risk for ED. In 71,849 men with benign prostatic hyperplasia (BPH), the risk of ED was not increased with the use of finasteride or dutasteride only (odds ratio [OR] 0.94), or a 5-alpha reductase inhibitor plus an alpha blocker (OR 0.92) compared with an alpha blocker only. In addition, the risk of ED was not increase in 12 346 men prescribed finasteride 1 mg for alopecia, compared with unexposed men with alopecia (OR 0.95). The risk of ED did increase with longer duration of BPH, regardless of drug exposure. 
Knowing about your history of ED will help your health provider learn if your problems are because of your desire for sex, erection function, ejaculation, or orgasm (climax). Some of these questions may seem private or even embarrassing. However, be assured that your doctor is a professional and your honest answers will help find the cause and best treatment for you.