With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Constipation may be caused by Tramadol.
text_B: Tramadol , sold under the brandname Ultram among others , is an opioid pain medication used to treat moderate to moderately severe pain .. opioid. opioid. pain medication. analgesic. pain. pain. When taken as an immediate-release oral formulation , the onset of pain relief usually occurs within about an hour .. pain. pain. It has two different mechanisms .. First , it works by binding to the μ-opioid receptor .. opioid. opioid. μ-opioid receptor. μ-opioid receptor. Second , it inhibits the reuptake of serotonin and norepinephrine .. reuptake. reuptake. serotonin. serotonin. norepinephrine. norepinephrine. It is often combined with paracetamol -LRB- acetaminophen -RRB- as this is known to improve the efficacy of tramadol in relieving pain .. pain. pain. paracetamol. paracetamol. Serious side effects may include seizures , increased risk of serotonin syndrome , decreased alertness , and drug addiction , although the risk of serotonin syndrome appears to be low .. serotonin. serotonin. serotonin syndrome. serotonin syndrome. drug addiction. drug addiction. Common side effects include  : constipation , itchiness and nausea , among others .. constipation. constipation. itchiness. puritis. A change in dosage may be recommended in those with kidney or liver problems .. It is not recommended in those who are at risk of suicide .. suicide. suicide. While not recommended in women who are breastfeeding , those who take it should not stop breastfeeding .. breastfeeding. breastfeeding. Tramadol is a synthetic opioid of the benzenoid class -LRB- it contains a benzene ring -RRB- .. opioid. opioid. benzene. benzene. In the body it is metabolized to O-desmethyltramadol , which is a more potent opioid .. opioid. opioid. Tramadol was launched and marketed as `` Tramal '' by the German pharmaceutical company Grunenthal GmbH in 1977 in West Germany , and 20 years later it was launched in countries such as the UK , US , and Australia .. pharmaceutical company. pharmaceutical company. Grunenthal GmbH. Grunenthal. West Germany. West Germany. It is marketed under many brand names worldwide .
related.