Sexual Health/Sexual Dysfunction
There are a number of problems that can arise in the act of sex, and these are known collectively as sexual dysfunctions.
Male Dysfunctions 
Males can suffer from a number of sexual dysfunctions, such as erectile dysfunction, or premature ejaculation.
Erectile Dysfunction 
Erectile dysfunction, or "ED" is the inability of the man to achieve or maintain an adequately hard erection. This can be caused by poor blood-flow to the genitals, hormone problems, psychological problems, and a variety of other issues. Men who have high blood pressure or high cholesterol are at risk for developing ED. Similarly, men who have large amounts of psychological stress may be unable to develop an erection. ED is known to be provoked by alcohol brewers droop, smoking and most recreational drugs. Some prescription drugs such as those used to control high blood pressure (hypertension) also cause ED
If the cause of ED is physical, Viagra can sometimes be used to help develop an erection. Viagra works by increasing the blood flow to the penis, and causing the penis to store more of that blood in the erectile tissue. ED is usually a symptom of something more serious, and Viagra should never be used without medical advice from a doctor. Speaking to a doctor about sexual dysfunction is often extremely embarrassing for the patient, but doctors are trained to listen and advise.
Premature Ejaculation 
Premature ejaculation occurs when a man ejaculates quickly, after little or no sexual contact, and sometimes without orgasm. After a man ejaculates, he may lose his erection quickly, and be unable to satisfy his partner. Premature ejaculation can be caused by a variety of physical and mental issues, and a doctor should be consulted on the best way to treat it. Premature ejaculation should not be confused with pre-emission - a natural lubricant sometimes produced by some men when sexually aroused,
Delayed Ejaculation 
Delayed Ejaculation is a condition where men are unable to ejaculate in a reasonable amount of time given "adequate" sexual stimulation. The average man will ejaculate in 5 minutes or less of active thrusting, and not being able to achieve orgasm in such a situation after a long period of time (or being unable to achieve one at all) is delayed ejaculation. A period of sexual abstinence and physical rest(three or four days) may help, but if the condition persists, medical advice is essential, as this may be a symptom of a more serious problem.
Female Dysfunctions 
Anorgasmia is a sexual dysfunction that can strike both males and females, but is significantly more common in females. Also, anorgasmia has almost never been studied in males, so there isn't enough data or statistics on that subject.
Anorgasmia is the inability to have an orgasm, under the influence of adequate sexual stimulation. Anorgasmia is highly related to delayed ejaculation in males, except delayed orgasm is marked by not being able to achieve orgasm in an acceptable timeframe, while anorgasmia is marked by being unable to achieve orgasm at all.
There is a studied link between anorgasmia and anti-depressant medications. Anorgasmia does not necessarily prevent conception.
The greatest obstacle to treatment of sexual disorders is the social embarrassment of speaking about very private matters to a public medical professional. The longer the problem is kept secret, the more difficult the treatment. Because satisfactory sexual function is dependent on good health, dysfunction often is a symptom of some unrelated medical or psychological condition which is likely to be a lot less sensitive to social castigation. Early medical consultation, preferably with your sexual partner for support, can often remedy the situation with only minor medicinal intervention, especially in young patients.