Do you ever think why the taste of chili peppers is spicy hot? It is due to the presence of capsaicin in a chili. Excessive intake of capsaicin causes burning and gastric irritation. But you may not believe that this heat-producing effect of capsaicin is effective in pain relief. These properties of capsaicin always attract researchers to do detail research on this phytochemical. The researchers had started their research long back. In 1876, researchers had first purified capsaicin and in 1919 the chemical structure of this herbal ingredient was derived.  After that, different research works continue to date to know more about this plant-derived active constituent.
Capsicum frutescens is a species of chili pepper, usually added in spicy recipes is our major dietary source of capsaicin. However, all plants belong to Capsicum genus that contains capsaicin as an active ingredient, except bell pepper (Capsicum annum). Capsaicin and other similar types of bioactive molecules group together and termed as capsaicinoids. The concentration of capsaicinoids differs from species to species.
Capsaicinoids concentration is relatively less in chili pepper i.e. 0.1 mg/g, red pepper contains little higher concentration 2.5 mg/g, whereas oleoresin red pepper contains 60 mg/g of capsaicinoids. Among different molecules present in capsaicinoids, capsaicin is present mainly in fruits, whereas other capsaicinoids found in leaves and stem of the plant. 
It has also been found that the consumption rate of capsicum species varies from region to region. The consumption rate is relatively low in India i.e. 2.5 g/person, in Mexico, it is quite high, i.e. 20g/person. The consumption rate in Thailand (5g/person) and in Saudi Arabia (15g/person) is moderate.
In capsicum fruits, placental tissue is surrounded by the seeds and concentration of capsaicin is high in this portion. Researchers noticed that capsaicin plays an important role in seed germination and gives protection against parasites. 
Capsaicin follows a variety of mechanisms of actions to impart different health benefits by regulating Transient receptor potential vanilloid 1 receptor activity. The following are the different mechanisms of actions proposed for different therapeutic benefits of capsaicin.
Supplementation of capsaicin is available in the market as a capsule, capsicum nasal sprays, and skin patch.
Capsaicin capsule: Individuals who do not like the raw form capsaicin or unable to tolerate the hot and spicy taste of capsaicin, they can intake Capsaicin capsule as a supplement.
Capsicum nasal sprays: This dosage form is recommended for treating non-allergic rhinitis and also providing symptomatic relief. Experts suggested that capsicum with 4 µg per puff dosing for thrice a day for three consecutive days is effective to control non-infectious, non-allergic, perennial rhinitis. 
Capsaicin patch: These patches are applied to the skin of the affected site. This patch usually recommended as an analgesic. Topical application of 8% capsaicin patch significantly decreases in post-herpetic neuralgia and post-traumatic neuropathic pain symptoms.
Capsaicin candy: This dosage form is effective to provide temporary relief from the pain associated with oral mucositis, which is a common side effect of chemotherapy or radiotherapy treatment. 
The presence of capsaicin in Capsicum genus plants helps in the following manner.
Apart from these general uses, the following are some expected therapeutic application of capsaicin.
Capsaicin for Neuropathy and Arthritis Pain
Capsaicin can counteract pain sensation as it regulates Transient receptor potential vanilloid 1 (TRPV1) receptor functioning. The local pain control ability of Capsaicin is effective to provide back pain relief and effective control of angina pain.  The analgesic property of Capsaicin effective to manage both neuropathic pain and chronic musculoskeletal pain. A clinical study reported that the analgesic property of Capsaicin can control post-herpetic neuralgia and diabetic neuropathy pain also. 
Capsaicin for Infection control
Herbal researchers expected that the anti-parasitic property of capsaicin is effective to control human infections also. 
Capsaicin for Diabetes-induced Hypertension
Diabetic patients often have hypertension problems. An animal research study conducted on diabetic mice reported that capsaicin is effective to reduce oxidative stress in blood vessels. Activation of TRPV1 by administering capsaicin leads to endothelium-dependent vasodilation. These effects improve hypertension in diabetic mice. This study result indicates that capsaicin may have a therapeutic benefit to prevent cardiac risk in diabetic patients. 
Capsaicin benefits heart
It is well proven that capsaicin activates TRPV1 and helps to provide benefits in cardiac muscle. The administration of capsaicin helps to combat against cardiac hypertrophy and fibrosis development. Therefore, capsaicin has a great benefit to prevent heart failure, as it controls metabolic disorders induced cardiac hypertrophy and fibrosis and simultaneously this bioactive phytochemical has an anti-hypertensive effect. [3,4]
Capsaicin benefits asthma
Beta-adrenergic medications are the drug of choice in the conventional treatment of asthma. Administration of capsaicin induces beta-adrenergic action by regulating energy metabolism. This has a direct influence on oxygen consumption and respiratory quotient.  This mechanism improves asthma condition.
Capsaicin benefits weight loss
Capsaicin moderately enhances energy expenditure, stimulates fat oxidation due to its thermogenic property and diminishes appetite. All these mechanisms are effective to control weight management. 
Protection from Gastric Ulcer
It is commonly recommended that capsaicin containing food items should be avoided for patients having gastric ulcers due to their spicy taste. However, a research paper reported that capsaicin has preventive and gastric ulcer healing properties. There is an ulcer protective effect of capsaicin-induced against non-steroidal anti-inflammatory drugs and alcohol exposure. This bioactive phytochemical has an inhibitory effect on gastric acid secretion. It also neutralizes the acidic environment in G.I tract by boosting mucus and alkali secretion. It also promotes blood circulation in gastric tissue. 
The daily recommended dose for capsaicinoids is 20 mg. The dosing is very important for capsaicin, as it is mentioned in a review paper that moderate consumption of capsaicin helps to prevent gastric cancer, whereas excessive daily take of capsaicin can cause gastric cancer. Therefore, moderate spicy food is good for health. It is recommended that 135 mg capsaicin intake per day causes gastric irritation and stomach discomfort.