the biggest thing that i noticed (and is probably the most prevalent one) is that you get cold easily and you get tired quickly from excercising or walking long distances. i use to take for an arrythmia daily but i dont anymore because im pretty physically active and i couldnt stand the fatigue. you get use to it somewhat though after a week or two. the other common ones i hear others complain about are nightmares, apathetic attitude (dont care about stuff as much), and getting lightheaded if you stand up quickly. there are others but those are the common ones. some people get lots of side effects, others dont notice any at all, everybody can react differently

Atenolol causes significantly fewer central nervous system side effects (depression, nightmares) and fewer bronchospastic reactions,[clarification needed] both due to its particular pharmacologic profile.

It was the main β-blocker identified as carrying a higher risk of provoking type 2 diabetes, leading to its downgrading in the United Kingdom in June 2006 to fourth-line agent in the management of hypertension.

In addition, β-blockers blunt the usual sympathetic nervous system response to hypoglycemia (i.e. sweating, agitation, tachycardia). These drugs therefore have an ability to mask a dangerously low blood sugar, which further decreases their safety and utility in diabetic patients.

Side effects include:
indigestion, constipation
dry mouth
dizziness or faintness (especially cases of orthostatic hypotension)
cold extremities
hair loss
impotence
rhinitis
depression
confusion
insomnia, nightmares
fatigue, weakness or lack of energy

These side effects may or may not be experienced, but if they are, you should notify your doctor.

More serious side effects can include:
hallucinations
low blood pressure (hypotension)
skin reactions, e.g. rash, hives, flaking of skin, worsening of psoriasis
sensation of 'pins and needles' hands or feet
irritated eyes, visual disturbances
difficulty hearing
difficulty speaking
unsteadiness when walking

Serious side effects may require urgent medical attention. Some of these side effects are rare and others (not mentioned in the above list) can occur in some people.

Asthma:
Atenolol is classified as a β1-selective (or 'cardioselective') drug, one that exerts greater blocking activity on myocardial β1-receptors than on β2 receptors in the lung. The β2 receptors are responsible for keeping the bronchial system open. If these receptors are blocked, bronchospasm with serious lack of oxygen in the body can result. However, due to its cardioselective properties, the risk of bronchospastic reactions if using atenolol is reduced compared to nonselective drugs as propranolol. Nonetheless, this reaction may also be encountered with atenolol at high doses. Although traditionally B-blockers have been contraindicated when a person carries a diagnosis of asthma, recent studies have revealed that at moderate doses selective B blockers such as Atenolol are well tolerated.
Provisional data suggests that antihypertensive therapy with atenolol provides weaker protective action against cardiovascular complications (e.g. myocardial infarction and stroke) compared to other antihypertensive drugs. In some cases, diuretics are superior. However, controlled studies are lacking.
Unlike most other commonly-used β-blockers, atenolol is excreted almost exclusively by the kidneys. This makes it attractive for use in individuals with end-stage liver disease.

Overdose:
Symptoms of overdose are due to excessive pharmacodynamic actions on β1 and also β2-receptors. These include bradycardia, severe hypotension with shock, acute heart failure, hypoglycemia and bronchospastic reactions. Treatment is largely symptomatic. Hospitalization and intensive monitoring is indicated. In early cases emesis can be induced. Activated charcoal is useful to absorb the drug. Atropine will counteract bradycardia, glucagon helps with hypoglycemia, dobutamine can be given against hypotension and the inhalation of a β2-mimetic as hexoprenalin or salbutamol will terminate bronchospasms. Blood or plasma atenolol concentrations may be measured to confirm a diagnosis of poisoning in hospitalized patients or to assist in a medicolegal death investigation. Plasma levels are usually less than 3 mg/L during therapeutic administration, but can range from 3–30 mg/L in overdose victims.