They’re completely separate things.
A drug is a typically organic substance that can impair physiological functioning or kill when given to the healthy population and a drug as medicine is a chemical composition that will repair your improper bodily functioning or you will die without it in an individual body, long term. Addicts may develop non-medicinal physical dependence but medically-obligated physical dependents are not addicts per se.
A drug user with medical physical dependence only can take a processed form of their medicine without the psychological effects (commonly a high) very happily whereas an addict would require the high, the specific form of drug is merely a trigger for the brain created by past memories of use by the amygdala. These extreme-intensity usage memories create many of the symptoms of withdrawal (psychosomatic) and delude the brain into believing it genuinely needs the drug e.g. claims marijuana is as healthy as a vitamin and the push to normalize (the societal danger of addict populations, social contagion and acceptability).
The sole cause of addiction beyond a doubt is beginning use in the first place. It is impossible to be addicted to (or physically dependent on) a substance the body (and brain) has never experienced. This is a self-selecting type of stupidity (hubris/arrogance) regularly found in teenagers (immature prefrontal cortex) because such users do not think or disbelieve their mind could be compromised by addiction. Their brains already create this illusion to necessitate the anticipated reward (high) prior to initial use or they wouldn’t take it (such as the processed form with no high). The foolproof layman method to test for addiction is simple: substance deprivation for a year. Prepare for a list of excuses.
A physical dependency is often created by doctors to treat patients with chronic conditions, usually chronic pain symptoms (ongoing). Addicts try to ape this category (some sincerely, others deceptively) but are increasingly thwarted by processed (reward-weakened) variants of their poison. Specific advocates for drug legalization ignore the essential fact of escalation and compensation. As part of the brain’s hedonic treadmill, it craves increasingly more of the reward from use, compelling drug users to harder toxins (harder reward, creating deeper addiction and physical damage) and this is the biological component of addiction that makes the habitual behaviour of use so challenging to physically extinguish from the brain.
Physical dependency creates withdrawal symptoms too but the patient’s individual physical needs (inc. not dying) and substance type distinguish this from addicts e.g. insulin to a diabetic.The human brain is connected to facilitate the reward response feedback loops because they are evolutionally guided by the basic needs to survive (food, water, sex) and this is why there is no such thing as a food addict, water addict or sex addict, merely people with impulse control issues seeking a social ‘displacement of responsibility’. Beyond these essential elements for the sustenance of our individual life and species general, anything chemical creating a vacuous boost in the reward system is a drug, whether you like it or not. Drug users resent the stigma for their activities whether or not their poison is legal (ethanol/alcohol, tobacco, marijuana, cocaine etc) because the positive emotional response loop (dopamine, serotonin release) caused by their usage memories creates defensive dissonance when challenged by non-users. Even polite persistent enquiry can sometimes trigger a psychotic episode where the patient is completely detached from reality and VERY DANGEROUS. This is why trained professionals intervene. In the latter stages, the drug/s become integrated into personal identity and extraction or therapeutic measures become unlikely to resolve the issue without constant medical care (rehabilitation facilities). Moreover, this reduces the risk of sudden death caused by the somatic shock of going ‘clean’ and allows overall physiological strength to be built up (reverse what the drugs did) while the problem is gradually resolved.
If a substance exists in a natural form within, say, a foodstuff, it is not addictive because food reward circuits are natural and normal and can never be extinguished. This is why milk (dairy), sugar, chocolate, chilli, coffee and caffeine ‘addiction’ is a misnomer. However, a person habitually needing a purified artificial version of these may constitute a non-medical physical dependence or perhaps a behavioural addiction e.g. alcoholism. Behavioural addictions require holistic (whole life) perspective for diagnosis e.g. someone who works online cannot be an internet addict if those hours online constitute their occupation (add to their success and life) and they can easily disconnect for a while. Behavioural addictions where they do exist are more accurately termed compulsions and relate to personality disorders or obsessions created by unmet needs. Substitution is the norm where one behaviour is broken, another is taken up. Social contagion is a significant factor for poor impulse control. Behavioural or result-based addictions when positive are discounted for lack of stigma nor bodily harm e.g. ‘high’ grades, promotion (power/status boost), painting. However, they can display withdrawal symptoms from endogenous neurotransmittor levels e.g. low serotonin creates acute compulsiveness completing the cycle to repeat a rewarding behaviour and low dopamine creates psychomotor agitation including pacing and fidgeting, also apathy, chosen social isolation and anhedonia (nothing is enjoyable and everything fast becomes boring).
Related terms: Dosage Response Curve and (innate) Arousal Thresholds causative of addictive personality tendency.
Mark the positive addiction withdrawal symptoms from endogenous behaviour-triggered stimulation.
And yes, you can be addicted to love.