for drawing blood for testing purposes, and 16- or 17-gauge needles are most commonly used for blood donation, as the resulting lower pressure is less harmful to red blood cells (it also allows more blood to be collected in a shorter time). Although reusable needles remain useful for some scientific applications, disposable needles are far more common in medicine. Disposable needles are embedded in a plastic or aluminium hub that attaches to the syringe barrel by means of a press-fit or twist-on fitting. These are sometimes referred to as "Luer Lock" connections, referring to the trademark Luer-Lok. The male and female luer lock and hub—produced by pharmaceutical equipment manufacturers—are two of the most critical parts of disposable hypodermic needles. Use by non-specialists Hypodermic needles are usually used by medical professionals (dentists, phlebotomists, physicians, pharmacists, nurses, paramedics), but they are sometimes used by patients themselves. This is most common with type one diabetics, who may require several insulin injections a day. It also occurs with patients who have asthma or other severe allergies. Such patients may need to take desensitization injections or they may need to carry injectable medicines to use for first aid in case of a severe allergic reaction. In the latter case, such patients often carry a syringe loaded with epinephrine (e.g. EpiPen), diphenhydramine (e.g. Benadryl), or dexamethasone. Rapid injection of one of these drugs may stop a severe allergic reaction. Multiple sclerosis patients may also treat themselves by injection; several MS therapies, including various interferon preparations, are designed to be self-administered by subcutaneous or intramuscular injection. In some countries, erectile dysfunction patients may be prescribed Alprostadil in injectable form, which is self-injected directly into the base or side of the penis with a very fine hypodermic needle. Hypodermic needles are also used by untrained users in recreational intravenous drug use (e.g., injecting solutions of heroin and water). Before governments attained current levels of awareness about the spread of disease through shared needles, hypodermic syringes in many countries were available only by prescription. Thus, in order to limit the spread of blood-borne diseases such as hepatitis and HIV through shared injection equipment, many countries have needle exchange programs in most larger cities. In some countries, such programs are wholly or partially subsidized by the government. Blunt needles, manufactured without a sharp bevel and usually non-sterile, are used industrially for filling small containers or accurately applying small amounts of