Is Maintenance or Switching Between Freebase and Nicotine Salt Liquid Associated with Electronic Nicotine Delivery Systems Dependence?

Figures & data

Table 1. Weighted sample characteristics by nicotine formulation switching status from wave 3 (September-November 2021) to wave 5 (February-April 2023) of the VAPER study (N = 543).

		Total (n = 543)	Nicotine Formulation Change Status from W3 (September–November 2021) to W5 (February–April 2023)
			All nicotine salt (n = 264, 49.3%)	All freebase (n = 187, 34.9%)	Changes in formulation (n = 85, 15.8%)
					Total	Freebase to salt (n = 54, 10.1%)	Salt to freebase (n = 17, 3.2%)	Changing back & forth (n = 13, 2.4%)
		n (%)	n (%)	n (%)	n (%)	n (%)	n (%)	n (%)
Geographic location**	Northeast	69 (12.7)	38 (14.2)	22 (11.5)	8 (9.4)	5 (10.0)	0 (0)	3 (19.7)
	Midwest	113 (20.8)	63 (23.8)	37 (19.7)	13 (15.7)	7 (13.7)	4 (23.5)	2 (13.6)
	South	209 (38.6)	107 (40.5)	69 (36.7)	33 (38.6)	22 (40.6)	5 (27.3)	6 (45.4)
	West	151 (27.9)	57 (21.5)	60 (32.1)	31 (36.3)	19 (35.8)	8 (49.1)	3 (21.3)
Age (p < 0.001)	21–29	147 (27.1)	91 (34.3)	26 (13.8)	27 (32.2)	19 (35.8)	7 (38.6)	1 (9.1)
	30–44	292 (53.7)	142 (53.6)	100 (53.2)	47 (55.6)	30 (54.4)	9 (49.9)	9 (68.1)
	45+	104 (19.2)	32 (12.1)	62 (32.9)	10 (12.2)	5 (9.8)	2 (11.6)	3 (22.8)
Age of First Use of ENDS (p = 0.010)	<21	110 (20.3)	67 (25.2)	21 (11.3)	19 (22.4)	14 (24.9)	4 (24.2)	1 (9.1)
	21+	433 (79.7)	198 (74.8)	166 (88.7)	66 (77.6)	41 (75.1)	13 (75.8)	12 (90.9)
Gender* (p = 0.858)	Man	306 (56.4)	143 (54.2)	111 (59.4)	48 (57.0)	30 (55.5)	10 (56.8)	8 (63.6)
	Woman	229 (42.2)	117 (44.3)	73 (39.1)	35 (41.9)	23 (42.7)	7 (43.2)	5 (36.4)
	Non-man/woman	7 (1.3)	3 (1.1)	3 (1.6)	1 (1.1)	1 (1.8)	0 (0)	0 (0)
	Prefer not to answer	1 (0.2)	1 (0.4)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)
Race* (p = 0.600)	White	489 (90.1)	235 (88.9)	172 (92.0)	76 (89.9)	49 (90.9)	16 (90.8)	11 (84.7)
	Non-white single race	19 (3.4)	8 (3.1)	7 (3.9)	3 (3.3)	1 (1.8)	1 (3.4)	1 (9.1)
	Multi race	30 (5.5)	17 (6.3)	7 (3.9)	5 (6.3)	4 (7.3)	1 (5.8)	1 (3.1)
	Prefer not to answer	5 (0.9)	4 (1.6)	1 (0.2)	1 (0.5)	0 (0)	0 (0)	1 (3.1)
Hispanic origin**	Yes	29 (5.3)	14 (5.3)	10 (5.4)	5 (5.4)	3 (6.3)	0 (0)	1 (9.1)
	No	508 (93.5)	248 (93.6)	176 (93.9)	78 (92.5)	49 (90.5)	17 (100.0)	12 (90.9)
	Prefer not to answer	6 (1.1)	3 (1.1)	1 (0.7)	2 (2.1)	2 (3.2)	0 (0)	0 (0)
Annual household income* (p = 0.488)	<$40,000	204 (37.6)	91 (34.5)	77 (41.1)	32 (37.9)	24 (44.8)	4 (24.9)	3 (25.8)
	$40,000–$59,999	126 (23.2)	69 (26.1)	40 (21.1)	17 (20.4)	7 (12.2)	6 (33.5)	5 (37.6)
	$60,000–$99,999	135 (24.8)	63 (24.0)	48 (25.8)	22 (26.0)	13 (24.8)	5 (26.7)	4 (30.4)
	$100,000 +	71 (13.1)	38 (14.3)	18 (9.7)	13 (15.2)	10 (18.1)	3 (14.9)	1 (3.1)
	Prefer not to answer	7 (1.4)	3 (1.1)	4 (2.3)	1 (0.5)	0 (0)	0 (0)	1 (3.1)
Sexual orientation**	Heterosexual or straight	184 (69.4)	184 (69.4)	147 (78.6)	61 (72.2)	38 (69.9)	10 (58.4)	13 (100.0)
	Non-heterosexual	79 (29.9)	79 (29.9)	33 (17.8)	20 (24.1)	14 (25.4)	7 (38.2)	0 (0)
	Prefer not to answer	2 (0.7)	2 (0.7)	7 (3.6)	3 (3.7)	3 (4.7)	1 (3.4)	0 (0)
Smoking status** (W5: February–April 2023)	Never smoker	65 (12.1)	32 (12.2)	20 (10.6)	11 (13.1)	10 (19.2)	1 (3.4)	0 (0)
	Former smoker	381 (70.4)	183 (69.3)	137 (73.6)	58 (68.8)	37 (67.2)	10 (57.2)	12 (90.8)
	Current smoker	95 (17.5)	49 (18.5)	29 (15.8)	15 (18.2)	7 (13.6)	7 (39.4)	1 (9.2)

Note. The numbers of participants reported in the table were weighted sample numbers scaled to the unweighted sample size. Due to rounding of the rescaled numbers, the sum of the column totals may not be exactly the same as the effective sample size. *The Rao-Scott chi-sq tests were conducted after excluding the “prefer not to answer” responses. **The Rao-Scott chi-sq test was not conducted due to the empty cells.

Table 2. ANCOVA models comparing ENDS dependence as a function of nicotine formulation switching status (N = 535).

ENDS dependence (EDS)	Total (n = 543)	Nicotine Formulation Change Status from W3 (September–November 2021) to W5 (February–April 2023)					Tests of Model Effects (DF = 6534)
		All nicotine salt (n = 264, 49.3%)	All freebase (n = 187, 34.9%)	Freebase to salt (n = 54, 10.1%)	Salt to freebase (n = 17, 3.2%)	Changing back & forth (n = 13, 2.4%)
	Mean (Std. error)	Mean (Std. error)	Mean (Std. error)	Mean (Std. error)	Mean (Std. error)	Mean (Std. error)
EDS in W3 (September–November 2021)	2.29 (0.04)	2.45* (0.06)	2.06* (0.07)	2.34 (0.12)	2.41 (0.25)	1.99 (0.31)	R-sq = 0.88; F = 530.49, p < 0.001
EDS in W4 (July–September 2022)	2.33 (0.04)	2.46* (0.06)	2.14*^,** (0.07)	2.47** (0.14)	2.38 (0.23)	1.96 (0.29)	R-sq = 0.88; F = 492.21, p < 0.001
EDS in W5 (February–April 2023)	2.42 (0.04)	2.59* (0.06)	2.18*^,** (0.08)	2.52** (0.12)	2.58 (0.20)	2.11 (0.31)	R-sq = 0.89; F = 567.21, p < 0.001
EDS change from W3 (September–November 2021) to W4 (July–September 2022)	0.04 (0.03)	0.002 (0.04)	0.08 (0.05)	0.13 (0.11)	−0.03 (0.11)	−0.04 (0.18)	R-sq = 0.02; F = 1.43, p = 0.200
EDS change from W4 (July–September 2022) to W5 (February–April 2023)	0.09 (0.03)	0.13 (0.04)	0.04 (0.04)	0.05 (0.11)	0.02 (0.13)	0.15 (0.08)	R-sq = 0.03; F = 3.01, p < 0.01
EDS change from W3 (September–November 2021) to W5 (February–April 2023)	0.13 (0.03)	0.13 (0.04)	0.12 (0.05)	0.19 (0.12)	0.17 (0.15)	0.11 (0.18)	R-sq = 0.05; F = 3.84, p < 0.01

Notes. *Significant difference between all nicotine salt and all freebase group at p < 0.001. **Significant difference between all freebase and freebase to salt group at p < 0.05.