A 33-year-old woman has symptoms of tiredness, constipation, and cold peripheries. What is the most likely diagnosis?

In this scenario, the symptoms of tiredness, constipation, and cold peripheries are strongly indicative of hypothyroidism. Hypothyroidism is characterized by a deficiency of thyroid hormones, which can lead to a range of symptoms due to a slow metabolic rate.

Tiredness and fatigue are common complaints in individuals with hypothyroidism, as the body's overall energy production is decreased. Constipation is also a frequent symptom because the slowing of metabolic processes can adversely affect gastrointestinal motility, leading to difficulties in bowel movements. Cold peripheries are attributed to reduced blood flow and lower metabolic heat production, as the metabolism slows down and the body's ability to generate heat is diminished.

Understanding hypothyroidism’s impact on body systems helps connect these symptoms. The overall picture presented aligns closely with this condition, making it the most likely diagnosis. The other conditions listed typically present with different symptomatology: hyperthyroidism often causes increased energy levels, weight loss, and heat intolerance; Crohn's disease typically involves abdominal pain, diarrhea, and weight loss; and Addison's disease can feature fatigue and other nonspecific symptoms but usually includes hyperpigmentation and low blood pressure rather than the mentioned symptoms.