that use of this medication by pregnant women can have an effect on the fetal heart, possibly resulting in fetal death via premature closing of the Ductus arteriosus. In October 2020, the U.S. Food and Drug Administration (FDA) required the drug label to be updated for all nonsteroidal anti-inflammatory medications to describe the risk of kidney problems in unborn babies that result in low amniotic fluid. They recommend avoiding NSAIDs in pregnant women at 20 weeks or later in pregnancy. Mechanism of action Indometacin, a non-steroidal anti-inflammatory drug (NSAID), has similar mode of action when compared to other drugs in this group. It is a nonselective inhibitor of cyclooxygenase (COX) 1 and 2, the enzymes that participate in prostaglandin synthesis from arachidonic acid. Prostaglandins are hormone-like molecules normally found in the body, where they have a wide variety of effects, some of which lead to pain, fever, and inflammation. By inhibiting the synthesis of prostaglandins, indometacin can reduce pain, fever, and inflammation. Indometacin mechanism of action, along with several other NSAIDs that inhibit COX, was described in 1971. Additionally, indometacin has recently been found to be a positive allosteric modulator (PAM) of the CB1 cannabinoid receptor. By enhancing the binding and signalling of endogenous cannabinoids such as anandamide, PAMs may elicit increased cannabinergic signalling in a tissue specific manner, reducing the incidence of problematic side effects such as psychoactivity while maintaining some antinociceptive activity. Besides, indometacin has logarithmic acid dissociation constant pKa of 3 to 4.5. Since the physiologic body pH is well above the pKa range of indometacin, most of the indometacin molecules will be dissociated into ionized form, leaving very little un-ionized form of indometacin to cross a cell membrane. If the pH gradient across a cell membrane is high, most of the indometacin molecules will be trapped in one side of the membrane with higher pH. This phenomenon is called "ion trapping". The phenomenon of ion trapping is particularly prominent in the stomach as pH at the stomach mucosa layer is extremely acidic, while the parietal cells are more alkaline. Therefore, indometacin are trapped inside the parietal cells in ionized form, damaging the stomach cells, causing stomach irritation. This stomach irritation can reduce if the stomach acid pH is reduced. Indometacin's role in treating certain headaches is unique compared to other NSAIDs. In addition to the class effect of COX inhibition, there is evidence that indometacin has