Wet cupping (hijama) – an ancient practice – is a form of alternative medicine that might be effective at treating certain medical conditions.
It was not an extraordinary thing when Michael Phelps, the most decorated Olympian of all time, won six medals at the 2016 Rio Olympics. The weird thing was he had dark circles in his back, on the shoulders and legs. At first many thought it was some sort of a rash; later it was learned that they were the temporary scars of a cupping therapy.
Usually practiced as an ancient form of alternative medicine, and criticized by some scientists as pseudoscience, according to recent research, cupping may have possible useful effects in removing heavy metals from the body  and on cardiac rhythm in terms of heart rate variability (HRV) .
An earlier study  also showed that wet cupping significantly reduced infarction. According to this paper, wet cupping therapy could help with recovery from strokes. The researchers had caused a stroke by tying up certain veins and then performed cupping on the animals. At the end of the study they examined the muscle layer of the heart that experienced the stroke and found that there was a significant reduction and recession in the area where heart muscle cells had died after the stroke. Equally interesting was the finding that the heart rhythm of the animals recovered after cupping.
"A recent animal study investigated the effects of wet cupping on hemodynamic variables, cardiac arrhythmias, and infarct size after myocardial ischemic reperfusion injury in male rats. Its results show that cupping did not change baseline heart rate or mean arterial blood pressure. Ischemic reperfusion injury caused an infarct size of 50%, whereas dry cupping and single and repeated wet cupping significantly reduced infarct size to 28%, 35%, and 22% of the area at risk, respectively. The rate of ischemia-induced arrhythmias was significantly modified by wet cupping." 
Another study  showed how the administration of cupping caused noticeable improvement in the heart rhythm of humans who’d suffered strokes. In this study, cupping therapy restored sympathovagal imbalances by stimulating the peripheral nervous system. Results showed “all HRV parameters increased after cupping therapy compared with before cupping therapy in healthy persons,” which indicates “for the first time in humans that cupping might be cardioprotective.”
Heavy metal poisoning
One problem facing humans is heavy metal poisoning. We take in poisons such as lead, mercury, cadmium, strontium, silver, and aluminum from the air, fruit and vegetables, and even seafood. Since no mechanism is available in the human body to break up and render harmless the metals, which are impossible for the kidneys to filter and discharge through urine, it is well established that an accumulation of heavy metals causes many illnesses, cancer among them, for which we do not even have a name.
The first phase of a study  conducted by a team of researchers at Turgut Ozal University found that heavy metals were present at much higher levels – sometimes as much as nine-times higher – in the blood sucked by wet cupping than in the blood taken from the arm. This finding suggests that toxic heavy metals that cannot be broken up by the liver can be discharged from the body via cupping. Since the body cannot get rid of heavy metals through normal metabolic processes, it accumulates them in subcutaneous tissues connected to the lymphatic system, which we can call a “temporary bin.” The carrying capacity of the subcutaneous lymphatic system is limited, and heavy metals can damage vital organs in the long run, so their evacuation through wet cupping would cause considerable relief. In a nutshell, wet cupping may help the kidneys clean out the blood.
The wet cupping recommended by the Prophet Muhammad, peace be upon him, is called hijama, which is somewhat different than other traditional types of cupping. In the hijama, vacuuming is performed, and a period of two-three minutes passes as toxins accumulate under the skin in the vacuumed area. Then cuts are performed on the ensuing swelling and the cups are emptied two or three times until the blood clots. The initial vacuuming has the effect of anesthesia. Pain in hijama is minimal, which allows hijama to have a similar effect to acupuncture. It is thought that hijama not only cleans the blood, but also stimulates the nerves.
In hijama, the vacuum power of cupping helps form a kind of fluid barrier between the cells gathering under the skin before a cut is made. This means that the cut is made in the upper layer of the skin into the fluid underneath, preventing any damage to capillaries.
The Prophet recommends to have hijama twice a year even if one does not feel ill.
Some claim wet cupping is beneficial but then claim that it is unnecessary, as the same benefits could be gained by letting blood through the arm. This claim is refuted by the possibility that there is a higher concentration of heavy metals and oxidative toxins in the blood sucked via wet cupping. As stated above, wet cupping helps discharge not only blood but also the motionless fluids stuck between tissues.
Giving blood is both useful and can help save lives. In addition to giving blood, wet cupping may also be useful for many health issues. The studies cited in this article need to be further consolidated by more research and scientific proofs to be able to suggest cupping as a medical procedure. Though it has been shown to be effective at treating pain, researchers need to study its usefulness for more serious conditions.