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Is erectile dysfunction due to psychological or physical factors? Healthy men have involuntary erections in the early morning and during REM sleep (a stage in the sleep cycle with rapid eye movements). Men with psychogenic erectile dysfunction (erectile dysfunction due to psychological factors such as stress and anxiety rather than physical factors) usually maintain these involuntary erections. Men with physical causes of erectile dysfunction (for example, atherosclerosis, smoking, and diabetes) usually do not have these involuntary erections. buy generic viagra online usa buy viagra online kamagra online com kamagra online pills Order viagra us is it illegal to buy generic viagra online viagra online Metabolism (breakdown) of sildenafil is slowed by aging, liver and kidney dysfunction, and concurrent use of certain medications (such as erythromycin -- an antibiotic, and protease inhibitors, for HIV). Slowed breakdown allows sildenafil to accumulate in the body and potentially may increase the risk of side effects. Therefore in men over 65, in men with substantial kidney and liver disease, and in men who also are taking protease inhibitors, the doctor will initiate sildenafil at a lower dose (25 mg) to avoid accumulation of sildenafil in the body. A protease inhibitor ritonavir (Norvir) is especially potent in increasing the accumulation of sildenafil, thus men who are taking Norvir should not take sildenafil doses higher than 25 mg and at a frequency of no greater than once in 48 hours. Order viagra us A recent study suggests an epidemiological association between chronic periodontitis (periodontal inflammation) and erectile dysfunction, similarly to the association between periodontitis and coronary heart diseases, and cerebrovascular diseases.[17] In all the three conditions (erectile dysfunction, coronary heart disease and cerebrovascular diseases), despite the epidemiological association with periodontitis, no causative connection has proved yet. One of the forms of phosphodiesterase is termed PDE5. The prescription PDE5 inhibitors sildenafil (Viagra), vardenafil (Levitra) and tadalafil (Cialis) are prescription drugs which are taken orally. They work by blocking the action of PDE5, which causes cGMP to degrade. Treatment depends on the cause. Exercise, particularly aerobic exercise is an effective treatment for erectile dysfunction.[20][better source needed] Therefore, men with these conditions should not use vardenafil without having these conditions evaluated and stabilized first. For example, men with uncontrolled high blood pressure should have their blood pressure controlled; and men with potentially life-threatening abnormal heart rhythms should have these rhythms controlled. cialis online viagra buy cialis online How should tadalafil (Cialis) be administered? The recommended starting dose of tadalafil for most patients is 10 mg taken orally approximately one hour before sexual activity. The dose may be adjusted higher to 20 mg or lower to 5 mg depending on efficacy and tolerability. The maximum recommended dosing frequency is once per day, although for many patients tadalafil can be taken less frequently since the improvement in erectile function may last 36 hours. Tadalafil may be taken with or without food.