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Withdrawal is defined by the WHO as:

Tolerance refers to the decreased effectiveness of a given drug with repeated administration.

The classic hallucinogens stimulate the serotinergic system, and specifically the 5HT_2A receptors (López-Giménez, González-Maeso, 2017), but fail to activate the reward centers in the brain. Indeed, all addictive drugs activate the reward circuitry of the brain, thereby producing the subjective “high” that the drug abuser seeks (Gardner, 2011). Tolerance to these drugs has rarely been reported (Smith et al., 1999) and LSD rarely produces serious withdrawal symptoms (source: LSD Abuse Help. But indeed, tolerance can develop, associated with 5HT_2A receptor downregulation (Gresch et al., 2005). An LSD tolerance can be developed quickly, although it usually dissipates within just a few days depending on the user, their dosages and frequency of use. Long term tolerances are uncommon because users do not frequently repeat doses of LSD without taking breaks in between (source: Hallucinogens).

Short answer
Withdrawal effects are generally associated with drugs that induce feelings of euphoria by stimulating the reward center of the brain, either directly (cocaine, morphine) or indirectly (alcohol, nicotine). The classic hallucinogens have little effect on the dopaminergic pathways and hence do not cause serious withdrawal effects as observed with other classes of psychoactive drugs.

Background
Withdrawal is defined by the WHO as:

Tolerance refers to the decreased effectiveness of a given drug with repeated administration.

The classic hallucinogens stimulate the serotinergic system, and specifically the 5HT_2A receptors (López-Giménez, González-Maeso, 2017), but fail to activate the reward centers in the brain. Indeed, all addictive drugs activate the reward circuitry of the brain, thereby producing the subjective “high” that the drug abuser seeks (Gardner, 2011). Tolerance to these drugs has rarely been reported (Smith et al., 1999) and LSD rarely produces serious withdrawal symptoms (source: LSD Abuse Help. But in rare cases, tolerance can develop and is associated with 5HT_2A receptor downregulation (Gresch et al., 2005) and the development of hallucinogen persisting perception disorder (HPPD). An LSD tolerance can be developed quickly, although it usually dissipates within just a few days depending on the user, their dosages and frequency of use. Long term tolerances are uncommon because users do not frequently repeat doses of LSD without taking breaks in between (source: Hallucinogens).

<sub>References
- Gardner, Adv Psychosom Med (2011); 30: 22–60
- Gresch et al., Neuropsychopharmacology (2005); 30: 1693–1702
- López-Giménez, González-Maeso, Curr Top Behav Neurosci (in press)
- Smith et al., Psychopharmacology (1999); 144(3): 248–54
- Stafford et al., Pharmacol Biochem Behav (2001); 69(1-2):233-7
- Stewart & Baidani, Behav Pharmacol (1993); 4(4): 289-312</sub>

The SSRIs you mention basically work by downregulation of presynaptic 5HT_1A receptors (Celeda et al., 2004), which are unrelated to the effects of hallucinogens.

<sub>References
- Celeda et al., J Psychiatry Neurosci (2004); 29(4): 252–65
- Gardner, Adv Psychosom Med (2011); 30: 22–60
- Gresch et al., Neuropsychopharmacology (2005); 30: 1693–1702
- López-Giménez, González-Maeso, Curr Top Behav Neurosci (in press)
- Smith et al., Psychopharmacology (1999); 144(3): 248–54
- Stafford et al., Pharmacol Biochem Behav (2001); 69(1-2):233-7
- Stewart & Baidani, Behav Pharmacol (1993); 4(4): 289-312</sub>

The classic hallucinogens stimulate the serotinergic system, and specifically the 5HT_2A receptors (López-Giménez, González-Maeso, 2017), but fail to activate the reward centers in the brain. Indeed, all addictive drugs activate the reward circuitry of the brain, thereby producing the subjective “high” that the drug abuser seeks (Gardner, 2011). Tolerance to these drugs has rarely been reported (Smith et al., 1999)

<sub>References
- Gardner, Adv Psychosom Med (2011); 30: 22–60
- López-Giménez, González-Maeso, Curr Top Behav Neurosci (in press)
- Smith et al., Psychopharmacology (1999); 144(3): 248–54
- Stafford et al., Pharmacol Biochem Behav (2001); 69(1-2):233-7
- Stewart & Baidani, Behav Pharmacol (1993); 4(4): 289-312</sub>

The classic hallucinogens stimulate the serotinergic system, and specifically the 5HT_2A receptors (López-Giménez, González-Maeso, 2017), but fail to activate the reward centers in the brain. Indeed, all addictive drugs activate the reward circuitry of the brain, thereby producing the subjective “high” that the drug abuser seeks (Gardner, 2011). Tolerance to these drugs has rarely been reported (Smith et al., 1999) and LSD rarely produces serious withdrawal symptoms (source: LSD Abuse Help. But indeed, tolerance can develop, associated with 5HT_2A receptor downregulation (Gresch et al., 2005). An LSD tolerance can be developed quickly, although it usually dissipates within just a few days depending on the user, their dosages and frequency of use. Long term tolerances are uncommon because users do not frequently repeat doses of LSD without taking breaks in between (source: Hallucinogens).

<sub>References
- Gardner, Adv Psychosom Med (2011); 30: 22–60
- Gresch et al., Neuropsychopharmacology (2005); 30: 1693–1702
- López-Giménez, González-Maeso, Curr Top Behav Neurosci (in press)
- Smith et al., Psychopharmacology (1999); 144(3): 248–54
- Stafford et al., Pharmacol Biochem Behav (2001); 69(1-2):233-7
- Stewart & Baidani, Behav Pharmacol (1993); 4(4): 289-312</sub>